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1
Khalili, Imad. "Sensibilité, sévérité et spécificités des explosions de mélanges hybrides gaz/vapeurs/poussières." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0088/document.
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La sensibilité et la sévérité d'explosion des différents mélanges gaz/vapeur-poussière ont été étudiées grâce à des dispositifs standards (sphère de 20 L, tube de Hartmann). Les spécificités des explosions de mélanges hybrides gaz/poussière ont été mises en évidence. En fait, même pour des concentrations de gaz inférieures à la limite inférieure d'explosivité (LIE), la probabilité d'inflammation et la gravité d'explosion peuvent être considérablement augmentées, ce qui permettra notamment de conduire à de grands changements dans la détermination des zones ATEX. Il a été, par exemple, démontré que ces mélanges peuvent être explosifs même lorsque la concentration en poudre et la concentration en vapeur sont respectivement en dessous de la concentration minimale explosive et de la LIE. En outre, des effets de synergie ont été observés et la vitesse de montée en pression de mélanges hybrides peut être supérieure à celles des gaz purs. Les origines de ces spécificités ne doivent pas être recherchées dans la modification d'un paramètre unique, mais peuvent probablement être attribuées aux effets combinés sur l'hydrodynamique (propagation de la flamme), le transfert thermique et la cinétique de combustion. Des expériences ont été menées afin de souligner l'importance de chaque contribution. Basé sur des schémas cinétiques classiques à coeur rétrécissant prenant en compte des diverses contraintes lors d'une réaction non-catalytique de gaz/solide et sur des modèles de combustion homogène pour les gaz, un modèle a été développé pour représenter l'évolution temporelle de la pression d'explosion pour ces mélanges<br>The explosion sensitivity and severity of various gas/vapor-dust mixtures have been studied thanks to specifically modified apparatuses based on a 20 L sphere and a Hartmann tube. The specificities of gas/dust hybrid mixtures explosions have been highlighted. In fact, even for gas concentrations lower than the lower explosivity limit (LEL), the ignition probability and the explosion severity can be greatly increased, which will notably lead to great changes in the Ex zones determination. For instance, it has been shown that such mixtures can be explosive when both the dust and gas concentrations are below their respective minimum explosive concentration and LEL. Moreover, synergistic effects have been observed and the rate of pressure rise of hybrid mixtures can be greater than those of the pure gases themselves. The origins of these specificities should not be sought in the modification of a single parameter, but could probably be attributed to combined impacts on hydrodynamics (flame propagation), thermal transfer and combustion kinetics. Experiments have been carried out in order to underline the significance of each contribution. Based on classical shrinking core models taking into account the various limitations during a non-catalytic gas/solid reaction and on homogeneous combustion for gases, a model has been developed to represent the time evolution of the explosion pressure for such mixtures
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Vanbersel, Benjamin. "Méthodes de raffinement de maillage automatique pour la simulation aux grandes échelles d'explosions de gaz." Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSEP085.
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La demande d’énergie ne cesse d’augmenter et est en grande partie obtenue grâce à la combustion, avec des carburants d’origine fossile ou renouvelable. Ces carburants, souvent stockés dans des environnements clos, présentent un danger en cas de fuite. En effet, l'inflammation d'un nuage de gaz pré-mélangé peut entraîner une explosion, provoquant une propagation rapide d'un front de flamme et générant des surpressions dangereuses pour les personnes et les infrastructures. Pour comprendre et prévenir ces explosions, diverses expérimentations sont menées, allant des tests en laboratoire aux simulations à l'échelle industrielle. Toutefois, les conditions extrêmes de température et de pression rendent les diagnostics précis difficiles à obtenir expérimentalement.La simulation numérique, notamment la simulation aux grandes échelles (LES) permet de compléter ces expérimentations en offrant une meilleure compréhension des phénomènes de combustion et de turbulence. La simulation LES a déjà prouvé son efficacité pour reproduire la dynamique des déflagrations et les surpressions associées dans des domaines de petite taille. Elle permet également des diagnostics précis à chaque point du domaine de calcul. Cependant, les grandes dimensions des installations industrielles posent des défis pour la résolution numérique complète des phénomènes physiques en jeu. La discrétisation homogène de tout le domaine de calcul serait trop coûteuse en termes de temps et de ressources. Ainsi, l'adaptation de maillage, particulièrement l'adaptation dynamique, est utilisée pour affiner la discrétisation dans les zones d'intérêt qui évoluent au fil du calcul. Cette technique permet de réduire la taille des maillages et les coûts de calcul en suivant les phénomènes d'intérêt prédéfinis durant leur propagation.Les travaux de cette thèse se concentrent sur le développement et la validation d'une méthode de raffinement adaptatif de maillage (AMR) pour les simulations LES des déflagrations, basée sur des critères physiques instantanés jouant un rôle important dans les explosions. La méthode proposée, nommée « Turbulent Flame Propagation-AMR » (TFP-AMR), reproduit la dynamique transitoire des flammes turbulentes et des structures tourbillonnaires dans l'écoulement et utilise la bibliothèque AMR non structurée kalpaTARU. Elle repose sur des critères dérivés des caractéristiques physiques des déflagrations, limitant la dépendance aux paramètres utilisateur. Un critère de sélection des vortex, issu de la théorie d'interaction flamme/vortex, et un critère spécifique d'adaptation de maillage sont développés pour garantir que les zones d'intérêt demeurent toujours dans une région de maillage raffiné tout au long du processus transitoire. La méthodologie est validée sur des cas élémentaires représentant des composantes fondamentales du problème, tels que la propagation de flamme, la propagation de vortex et l'interaction flamme-vortex.Enfin, la méthode est appliquée à des configurations de déflagrations, d’abord dans une chambre obstruée semi-confinée, puis dans un canal obstrué entièrement confiné, avec diverses variations paramétriques concernant la géométrie de la chambre et les propriétés du mélange initial. Dans ces configurations, la déflagration peut atteindre des régimes rapides, avec des formations d'ondes de choc en amont du front de flamme. Les comparaisons entre expériences et simulations démontrent que la méthode TFP-AMR obtient des résultats précis à un coût de calcul inférieur par rapport aux simulations de référence maillages statiques, en nécessitant que peu d’ajustement de paramètres, validant ainsi la robustesse et l'efficacité de la méthode pour ce type d’application<br>The global energy demand continues to rise, and is largely met through combustion, using fossil or renewable fuels. These fuels, often stored in enclosed environments, pose a significant hazard in the event of a leak. The ignition of a premixed gas cloud can lead to an explosion, causing rapid flame front propagation and generating dangerous overpressures that threaten both human life and infrastructure integrity. To understand and prevent these explosions, various experiments are conducted, ranging from laboratory tests to industrial-scale simulations. However, extreme conditions of temperature and pressure make it challenging to obtain accurate diagnostics experimentally.Numerical simulation, especially Large Eddy Simulation (LES), complements these experiments by providing a better understanding of combustion and turbulence phenomena at stake. LES has already proven effective in replicating the dynamics of deflagrations and the associated overpressures in small domains. It also allows for precise diagnostics at every point within the computational domain. However, the large dimensions of industrial installations raise challenges for a complete numerical resolution of the physical phenomena involved. An homogeneous discretisation of the entire computational domain would be too costly in terms of return time and computational resources. Therefore, mesh adaptation, particularly dynamic adaptation, is used to refine the discretisation in regions of interest that evolve during the calculation. This technique helps reduce mesh size and computational costs by tracking predefined phenomena of interest during their propagation.This thesis focuses on the development and validation of an adaptive mesh refinement (AMR) method for LES simulations of deflagrations, based on instantaneous physical criteria relevant to explosions. The proposed method, called "Turbulent Flame Propagation-AMR" (TFP-AMR), reproduces the transient dynamics of turbulent flames and vortical structures in the flow, and relies on the unstructured AMR library kalpaTARU. The method relies on criteria derived from the physical characteristics of deflagrations, minimising reliance on user-dependent parameters. In particular, a vortex selection criterion is derived from flame/vortex interaction theory. A specific mesh adaptation triggering criterion is also developed to ensure that regions of interest remain within a refined mesh zone throughout the transient propagation process.The methodology is validated on fundamental cases representative of the essential physical bricks of the problem, such as flame propagation, vortex propagation, and flame-vortex interaction. Finally, the method is applied to deflagration configurations. A semi-confined obstructed chamber is first considered, with extensive parametric variations regarding the chamber geometry and the initial mixture properties. A fully confined obstructed channel is then considered, where deflagration can reach high-speed regimes with shock waves forming ahead of the flame front. Comparisons between experimental and simulation results demonstrate that the TFP-AMR method achieves accurate results at a lower computational cost compared to static mesh reference simulations, while requiring minimal parameter adjustments. These application cases validate the method robustness and effectiveness for such applications
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Caillol, Christian. "Influence de la composition du gaz naturel carburant sur la combustion turbulente en limite pauvre dans les moteurs à allumage commandé." Aix-Marseille 1, 2003. http://www.theses.fr/2003AIX11042.
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L'influence des composants minoritaires majeurs intervenant dans la composition du gaz naturel est quantifiee experimentalement. La base de donnees constituee met en evidence l'influence significative de la nature du gaz sur les performances energetiques et environnementales du moteur. Un modele de combustion predictif a une zone, base sur la resolution numerique des equations de conservation de l'energie et des especes et integrant une cinetique chimique detaillee est mis en Œuvre. Afin de prendre en compte les effets de la turbulence, une approche thermodynamique predictive a deux zones est ensuite adoptee. La propagation de la flamme de premelange est decrite dans un premier temps par une loi de comportement, puis par une formulation du taux de consommation du combustible gouverne par le melange turbulent. Enfin, une modelisation de la formation du monoxyde d'azote, basee sur l'utilisation d'une fonction de densite de probabilite de la temperature dans les gaz brules, est proposee<br>The influence of the main minor components involved in natural gas composition, ethane and propane, is experimentally quantified. The constituted experimental database demonstrates the significant effect of fuel mixture properties on engine performance and pollutant emission levels. A one-zone predictive combustion model, based on the numerical resolution of energy and species conservation equations, which integrates detailed chemical kinetics, is developed. In order to take into account the effects of turbulence on the combustion process, a two-zone predictive thermodynamic approach is then adopted. The premixed flame propagation is first described by an empirical burning law, then by an expression for the rate of combustion of fuel controlled by the turbulent mixing process. Finally, a numerical modeling approach of nitric oxide formation, based on the use of a probability density function of temperature in burnt gases, is proposed
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Mercier, Marc. "Contribution à l'étude du fonctionnement d'un moteur à allumage commandé alimenté au gaz naturel de Groningue." Valenciennes, 2006. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/14577380-5929-49d9-bd99-fb1d1dc8381f.
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Le but de cette thèse est d’étudier le fonctionnement d’un moteur à allumage commandé alimenté au gaz naturel de Groningue et à l’essence afin de déterminer si le gaz naturel est un carburant alternatif à l’essence attrayant. Ce travail expérimental a été précédé du développement d’un banc d’essai spécifique. Dans un premier temps, l’analyse des performances du moteur a été abordée par l’étude du couple en fonction de la richesse, de la vitesse de rotation et de l’avance à l’allumage. Nous avons étudié les températures de fonctionnement du moteur ainsi que les températures d’échappement. De ce travail, nous avons ciblé les paramètres influençant majoritairement le comportement du moteur tels l’avance et la richesse. On enregistre une baisse de la valeur du couple au gaz naturel. Nous avons abordé par la suite l’étude de la pression cylindre, ce qui a été rendu possible par l’équipement du moteur d’un capteur de pression du type piézo-électrique dont le signal est acquis par le biais d’une baie d’acquisition rapide. Le gaz présente une plage de fonctionnement en richesse plus large qu’à l’essence. Les délais d’inflammation et durées de combustion sont augmentés au gaz ce qui nécessite un décalage d’avance accrue par rapport à l’essence pour l’obtention d’une PMI maximale. Nous avons réalisé la modélisation du délai et de la durée de combustion en fonction de la richesse. La dispersion cyclique de la pression cylindre fait l’objet de la troisième partie de ce mémoire. La stabilité de fonctionnement du moteur est optimal lorsque l’avance à l’allumage et la richesse sont réglées de manière à obtenir le couple maximal. Les charges partielles influencent de façon majeure les paramètres de fonctionnement du moteur en modulant la masse d’air admise dans les chambres de combustion en modifiant la pression de l’air du collecteur d’admission. Le couple obtenu à l’essence reste élevé pour des charges partielles à partir de la demie charge. Le couple au gaz naturel chute en dessous de trois quart de charge. Cependant le gaz présente une dispersion cyclique faible face à l’essence. Les taux d’émission de CO2, CO, HC au gaz sont plus faibles qu’à l’essence<br>We studied the performance of a spark ignition engine fuelled with natural Groningen gas and compared the obtained results with those given when using gasoline. The analysis was made versus rotational speed, spark ignition timing and equivalence ratio with simultaneous measurements of cylinder head and exhaust temperatures. The cylinder pressure recording show the possibility of working with poor mixtures in the case of natural gas. The ignition delays and combustion durations are higher with gas and imply the necessity of an increased spark timing in comparison with gasoline to maximize the mean effective pressure. We calculated the combustion temperatures and the ignition delays and combustion durations were modelled versus equivalence ratio. The cylinder pressure cyclic dispersion showed that the combustion stability is optimum for spark timings and equivalence ratio corrsponding to maximum torques. With these conditions, the combustion durations are minimum with a fast front flame propagation and maximum mean effective pressure. Part loads influence the performance data by adjusting the admitted air flow in the admission pipe. The torque with gasoline remains high up to half load whereas the torque with natural gas decreases quickly below three quarter load. The polluant emissions are weakes with natural gas. Natural gas is an attractive alternative solution for engines fitted to this type of fuel
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Brecq, Guillaume. "Contribution à la caractérisation thermodynamique du cliquetis dans les moteurs à gaz : application à de nouvelles méthodes de détection." Nantes, 2002. http://www.theses.fr/2002NANT2064.
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Le gaz naturel représente un carburant prometteur alliant performances énergétiques et faibles émissions polluantes. Contrairement aux carburants liquides dont la qualité est maîtrisée, celle du gaz naturel dépend de son origine et est donc amenée à varier dans un réseau interconnecté. Pour des réglages prédéfinis du moteur, ces variations de qualité peuvent conduire à une combustion anormale (auto-inflammation de la charge fraiche. Ce phénomène, caractérisé par un bruit métallique, est appelé cliquetis. Un cliquetis intense provoque une dégradation des performances et conduit à des dégats importants, s'il n'est pas rapidement contrôlé. Le cliquetis constitue un obstacle pour l'optimisation des performances énergétiques des moteurs à gaz couplée à la réduction de la pollution atmosphérique. Le développement d'outils permettant sa maîtrise est l'objectif visé par ce travail. Dans cette optique, un modèle thermodynamique à "deux zones" a été développé et adapté à la caractérisation du cliquetis. Il est basé sur une loi comportementale de la combustion, fonction des paramètres moteur et de la qualité du gaz. . .
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Sorin, Anthony. "Étude de l'interaction solide - fluide dans la zone d'entrée d'un tube cylindrique support d'un écoulement d'air intermittent : application à l'étude thermique des collecteurs d'échappement de moteurs à explosion." Nantes, 2003. http://www.theses.fr/2003NANT2069.
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Ce travail concerne l'étude expérimentale de l'interaction thermique entre la paroi d'un canal cylindrique droit et un écoulement intermittent d'air chaud en régime périodique établi. Cette étude trouve son application première dans le développement de nouvelles lignes d'échappement de véhicules automobiles. Le principe de mesure est fondé sur un modèle axisymétrique simple, de zone d'entrée, qui fait appel au couplage, conduction dans le solide, convection dans le fluide. L'estimation du coefficient de transfert paroi - écoulement intermittent se fait au moyen d'une technique inverse fondée sur la méthode du gradient conjugué. . .
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Zadnik, Martin Vingerhoeds Rob A. Vincent François. "Détection du cliquetis pour moteur automobile." Toulouse (Université Paul Sabatier, Toulouse 3), 2008. http://thesesups.ups-tlse.fr/206.
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Royer, Pascale. "Contribution de l'homogénéisation à l'étude de la filtration d'un gaz en milieu déformable à double porosité : application à l'étude du système gaz-charbon." Université Joseph Fourier (Grenoble ; 1971-2015), 1994. http://www.theses.fr/1994GRE10186.
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L'objet de cette etude est de determiner, par la methode des developpements asymptotiques, des modeles mathematiques macroscopiques decrivant l'ecoulement d'un fluide compressible dans un milieu poreux a double porosite. Les limites des modeles classiques sont definies pour le cas particulier d'un milieu a double conductivite et une correction simple, elargissant leur domaine de validite, est proposee. Une adaptation de la methode des developpements asymptotiques pour le cas des milieux a double porosite est ensuite mise au point. Elle s'appuie sur l'existence de trois longueurs caracteristiques introduites par la geometrie du milieu. Alors que les methodes classiques considerent que le fluide est faiblement compressible, cette methode est appliquee ici pour etudier la filtration d'un fluide tres compressible dans un milieu poreux fracture. Le cas d'une matrice rigide, puis celui d'une matrice deformable, sont successivement envisages. Il s'avere que les comportements macroscopiques obtenus dependent des ordres de grandeur relatifs des rapports d'echelles. L'une des descriptions obtenues pour une matrice rigide est fortement non-lineaire et comporte des effets de memoire. L'etude pour une matrice deformable met en evidence la necessite de considerer separement les phenomenes de compressibilite du fluide et de deformabilite de la matrice. En guise d'application, l'etude du systeme gaz-charbon est alors envisagee, dans le but de contribuer a la prevention d'un phenomene dynamique se produisant dans les mines de charbon: le coup de poussier. Une description detaillee des differents processus qui se developpent au sein d'un milieu gaz-charbon, notamment le phenomene de sorption et ses consequences, est presentee et se fonde sur de nombreux resultats experimentaux. Enfin, en se basant sur l'etude theorique precedente, un modele de filtration avec adsorption d'un gaz dans un milieu poreux fracture rigide est propose
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Corre, Christian. "Structure d'une flamme en deux stades de butane : action d'un additif antidétonant : la n-méthylaniline." Lille 1, 1991. http://www.theses.fr/1991LIL10081.
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L'étude de l'oxydation du butane sur brûleur à flamme plate a été effectuée pour la première fois au-dessus de la pression atmosphérique (1. 4 bar pour une flamme froide seule et 1. 8 bar pour une flamme en deux stades). L'emploi de la chromatographie en phase gaz, de la résonance paramagnétique électronique, de la polarographie et de la colorimétrie ont permis la détermination plus de 46 profils d'espèces. Les propriétés antidétonantes de la N-méthylaniline ont également été démontrées par son action très importante sur la flamme de deuxième stade
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Kosiwczuk, Wenceslas. "Mesure simultanée des vitesses des gouttes et du gaz en mélange diphasique par PIV et fluorescence." Rouen, 2006. http://www.theses.fr/2006ROUES065.
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Zadnik, Martin. "Détection du cliquetis pour moteur automobile." Toulouse 3, 2007. http://thesesups.ups-tlse.fr/206/.
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Le cliquetis dans les moteurs automobiles est un phénomène parasite de combustion anormale avec de nombreuses conséquences néfastes. Cette thèse concerne de nouvelles techniques de traitement du signal issu du capteur cliquetis afin d'améliorer la détection. Dans un premier temps, nous analysons les caractéristiques du signal cliquetis par des méthodes temps-fréquence. Ensuite, l'utilisation de réseaux neuronaux est envisagée pour essayer de reconstruire le signal de pression intra-cylindre, car celui-ci est un meilleur indicateur du phénomène. La partie majeure de la thèse étudie différents détecteurs du cliquetis en se basant sur un modèle paramétrique du signal. Nous proposons plusieurs méthodes robustes, d'une part pour réduire la charge calculatoire et d'autre part pour rendre le traitement tolérant vis-à-vis de la connaissance imprécise des fréquences de résonance spécifiques au cliquetis. Nous effectuons le calcul des performances théoriques des différents détecteurs ainsi qu'une application de ces détecteurs aux signaux réels.<br>Knocking in automobile engines is a parasite phenomenon of abnormal combustion with several harmful consequences. This thesis is concerned with new techniques of knock sensor signal processing whose aim is to improve the detection. We first analyse the knock signal properties by means of time-frequency methods. Further on, the use of neural networks is considered in order to try to reconstruct the in-cylinder pressure signal, since this one better indicates the phenomenon. In the main part of the thesis, different knock detectors are studied, based on a parametric signal model. We propose various robust methods, on one hand to reduce the computational cost and on the other hand to assure a processing that is tolerant to imprecisely known knock- specific resonant frequencies. We derive theoretical detection performance of different detectors as well as apply these detectors on real signals
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Pak, Sun. "Adaptation, combustion et limites pauvres d'un moteur à allumage commandé au gaz naturel obtenu par conversion d'un diesel faible puissance." Valenciennes, 1994. https://ged.uphf.fr/nuxeo/site/esupversions/1d663861-db36-4829-9d80-aa7826a05ebe.
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Un moteur diesel faible puissance a était converti en A. C. Puis alimenté au gaz naturel. Les caractéristiques générales de la combustion (délais, durées de combustion, dispersion cyclique) ont été étudiées en fonction du rapport air-gaz, de l'avance à l'allumage, et du type de bougie ainsi que les performances du moteur. Pour le comportement en mélange très pauvre, nous avons déterminé les limites opératoires, analyse le déroulement de la combustion et observe les variations de pression. En utilisant un générateur de turbulence en forme de cône, nous avons reculé les limites pauvres et réduit la dispersion cyclique et la pollution estimée en fonction de la richesse du mélange, de l'avance à l'allumage, de la vitesse et de la charge du moteur. A la fin de l'étude, nous donnons les conditions opératoires optimum pour différentes charges et vitesses.
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Delorme, Rodolphe. "Applications des décharges de type streamer nanoseconde aux domaines de la combustion et de la spectroscopie." Rouen, 2004. http://www.theses.fr/2004ROUES007.
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Ce travail de thèse porte sur l'application de décharges haute-tension, ayant des temps de montée de l'ordre de la nanoseconde, dans des domaines en pleine expansion actuellement. Cette étude s'articule autour de deux grands axes de recherche que sont la combustion et la spectroscopie. La première des applications potentielles dans le domaine de la combustion, l'allumage d'un mélange combustible en configuration pointe-couronne, nous a permis de valider cette technique d'allumage et de la comparer à un allumage classique par étincelle. Ce type d'allumage permet d'initier la combustion d'un mélange propane-air à richesse 1, à température ambiante, pour des pressions comprises entre 1 et 7 bars. La seconde application concerne la stabilisation de flamme liftée turbulente en sortie d'injecteur, par un plan de décharge en configuration fil-fil à barrière diélectrique. Ce procédé permet, pour une hauteur de stabilisation donnée, d'augmenter la vitesse débitante de près de 80%. L'énergie électrique injectée dans les décharges streamer correspond à 1/1000ème de l'énergie de la flamme. La limitation technique actuelle de ce type de stabilisation se situe au niveau de la fréquence de répétition des décharges (< 300 Hz). Dans le domaine de la spectroscopie, l'application de décharges streamer, en configuration fil-fil à barrière diélectrique, dans un mélange Argon-Hydrogène, permet de générer une émission entre 185 et 350 nm due à la transition dissociative de H2 (a3S+g-->b3S+u). L'ajout d'un gaz tampon, l'Hélium, permet d'accroître de 50% l'efficacité de la source<br>This thesis work concerns the application of high-voltage discharges, having rise time about the nanosecond, in fields in full expansion nowadays. This study is articulated around two large research orientations which are combustion and spectroscopy. The first of the potential applications in the field of combustion, the ignition of a combustible mixture in configuration point-to-crown, enabled us to validate this technique of ignition and to compare it with a traditional ignition by spark. This type of ignition makes it possible to initiate the combustion of a stoechiometric propane-air mixture, at ambient temperature, for pressures ranging between 1 and 7 bars. The second application relates to the stabilization of turbulent lifted flame at exit of injector, by a discharge sheet in wire-wire configuration with dielectric barrier. This process allows, for a height of stabilization given, to increase the flowing speed of almost 80%. The electric power injected into the streamer discharges corresponds to 1/1000th of the flame energy. The current technical limitation of this type of stabilization is at the level of the discharges repetition rate (< 300 Hz). In the field of spectroscopy, the application of streamer discharges, in wire-wire configuration with dielectric barrier, in a Argon-Hydrogen mixture, makes it possible to generate an emission between 185 and 350 nm due to the dissociative transition from H2 (a3S+g-->b3S+u). The addition of a buffer gas, Helium, makes it possible to increase by 50% the source efficiency
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Jérisian, Robert. "Comportement de frittés et de films d'oxyde de titane en présence de mélanges gazeux CO-CO2-O2-Ar hors équilibre thermodynamique : mise au point de capteurs résistifs pour la régulation de combustions." Tours, 1990. http://www.theses.fr/1990TOUR4003.
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Des capteurs en TiO2, sous forme de céramique, de couche épaisse obtenue par sérigraphie et de couche mince obtenue par pulvérisation cathodique, ont été étudiés sous l'action de flux gazeux en CO-CO2-O2-Ar hors équilibre thermodynamique. En régime stationnaire sous atmosphère oxydante autour de 600oc la résistance des capteurs suit la loi Po2 ½ P0,5/pco0,5 et autour de 830 oc la loi Po2 ½ Pc0 1/2 5. Sous atmosphère réductrice, dans l'intervalle de 600 à 830 oc, la réponse des échantillons massifs suit la loi (p c o 2/ p c o) 0,5 et celle des couches la loi fp o 2 0, 5 avec f fonction du taux de recouvrement (o a d s/sites de surface). En régime transitoire le temps de réponse des films de tio 2 dépend, lors d'un échelon de o 2, de la vitesse de diffusion de o 2 à travers la couche et, lors d'un échelon de Co, de l'interaction gaz-solide. Les couches obtenues par pulvérisation cathodique ont des constantes de temps de réponse de l'ordre de 30 MS.
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Lebel-Simon, Murielle. "Mesures simultanées par DRASC de température et de concentration de CO2 dans un moteur. Application à l'étude des variations cycle à cycle liées aux gaz résiduels." Rouen, 1994. http://www.theses.fr/1994ROUES010.
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Des mesures simultanées, par diffusion Raman anti-Stokes cohérente, de température et de concentration de CO2 ont été effectuées dans la chambre de combustion d'un moteur. L'objectif de cette étude est d'estimer l'influence des gaz résiduels sur les variations cycle à cycle de la combustion. Les mesures ont été effectuées en fonction de la richesse, de la vitesse de rotation, de la charge, du type de carburant et de la position du (ou des) point(s) d'allumage. La concentration de gaz résiduels au voisinage de la bougie juste avant l'allumage est un paramètre important sur la durée de la phase d'initiation. Durant la phase de propagation l'effet de la température des gaz brûlés l'emporte sur l'effet de dilution, une concentration plus élevée en gaz résiduels favorise la combustion. Dans le cas de combustion stoechiométrique ou riche, il semble que l'effet bénéfique de la température l'emporte; dans le cas de combustion pauvre, les deux effets initiation/propagation se compensent
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Lezzar, Balahouane. "Contribution à l'étude de la combustion et des limites de fonctionnement dans un monocylindre à taux de compression variable alimenté au méthane, au gaz de groningue et avec un mélange méthane-éthane." Valenciennes, 1987. https://ged.uphf.fr/nuxeo/site/esupversions/0d1a9c0a-0df4-4fab-8206-316c90031798.
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Corot, Théo. "Simulation numérique d'ondes de choc dans un milieu bifluide : application à l'explosion vapeur." Thesis, Paris, CNAM, 2017. http://www.theses.fr/2017CNAM1125/document.
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Cette thèse s'intéresse à la simulation numérique de l'explosion vapeur. Ce phénomène correspond à une vaporisation instantanée d'un volume d'eau liquide entraînant un choc de pression. Nous nous y intéressons dans le cadre de la sûreté nucléaire. En effet, lors d'un accident entraînant la fusion du cœur du réacteur, du métal fondu pourrait interagir avec de l'eau liquide et entraîner un tel choc. On voudrait alors connaître l'ampleur de ce phénomène et les risques d'endommagements de la centrale qu'il implique. Pour y parvenir, nous utilisons pour modèle les équations d'Euler dans un cadre Lagrangien. Cette description a l'avantage de suivre les fluides au cours du temps et donc de parfaitement conserver les interfaces entre l'eau liquide et sa vapeur. Pour résoudre numériquement les équations obtenues, nous développons un nouveau schéma de type Godunov utilisant des flux nodaux. Le solveur nodal développé durant cette thèse ne dépend que de la répartition angulaire des variables physiques autour du nœud. De plus, nous nous intéressons aux changements de phase liquide-vapeur. Nous proposons une méthode pour les prendre en compte et mettons en avant les avantages qu'il y a à l'implémentation de ce phénomène dans un algorithme Lagrangien<br>This thesis studies numerical simulation of steam explosion. This phenomenon correspond to a fast vaporization of a liquid leading to a pressure shock. It is of interest in the nuclear safety field. During a core-meltdown crisis, molten fuel rods interacting with water could lead to steam explosion. Consequently we want to evaluate the risks created by this phenomenon.In order to do it, we use Euler equations written in a Lagrangian form. This description has the advantage of following the fluid motion and consequently preserves interfaces between the liquid and its vapor. To solve these equations, we develop a new Godunov type scheme using nodal fluxes. The nodal solver developed here only depends on the angular repartition of the physical variables around the node.Moreover, we study liquid-vapor phase changes. We describe a method to take it into account and highlight the advantages of using this method into a Lagrangian framework
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Fakandu, Bala Mohammed. "Vented gas explosions." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/7340/.
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This investigation generated new experimental data on premixed gas/air vented explosions. A small (0.01 m3) and medium scale (0.2 m3) cylindrical vessels were used with L/D of 2.8 and 2 respectively, with range of vent area coefficients Kv of 2.7-21.7. The initial set of experiments considered free venting, so that the flame propagation during the venting process was laminar and also the short distance of the vessels would reduce the effects of flame self-accelleration. Covered vents were later used with vent static burst pressure Pstat from 35 to 450mb in the 10L vessel. Different gas mixtures were used throughout this work including methane-air (10%), propane-air (4 and 4.5%), ethylene-air (6.5 and 7.5%), and hydrogen-air (30 and 40%) gas mixtures. The ignition position at the far end opposite the vent and central location mid-way the length of the vessels were compared. Current venting guidance is based on experimental vented explosions with central ignition, but this work shows that end ignition opposite the vent is the worst case. The current design procedures for the protection of explosions using venting is shown to be inadequate for hydrogen-air explosions. New data has been presented which indicates that for hydrogen explosions, the vent flow behaves differently as compared to other gas mixtures investigated. Hence, the need for more research in hydrogen-air mixtures in order to have better understanding of hydrogen venting process. Experimental data from the current work also shows that multiple vents and vent shapes have significant effects on explosion overpressure and flame speeds. This is contrary to the assumption of the current venting standards. The effect of static burst pressure on explosion venting was shown to be quite different to that in the design standards, which is supported by other work in larger vessels. Other aspects of vent design that the standards say are not important were shown to be significant: the number of vents, the position of the vent, the shape of the vent, the ignition position. Laminar flame venting theory was shown to be a good predictor of the results and those from the literature where larger vessels were used.
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Kasmani, Rafiziana Md. "Vented gas explosions." Thesis, University of Leeds, 2008. http://etheses.whiterose.ac.uk/1604/.
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Explosion venting technology is widely accepted as the effective constructional protection measures against gas and dust explosions.The key problem in venting is the appropriate design of the vent area necessary for an effective release of the material i.e. the pressure developed during explosion did not cause any damage to the plant protected.Current gas explosion vent design standards in the USA (NFPA68, 2002) and European (2007) rely on the vent correlation first published by Bartknecht in 1993 (Siwek, 1996).N FPA 68 also recommends the correlation of Swift (Swift,1983)at low overpressures. For a vent to give no increase in overpressure other than that due to the pressure difference created by the mass flow of unburnt gases through the vent, the vent mass flow rate is assumed to be equal to the maximum mass burning rate of the flame and this consideration should be used as the design mass flow through the vent. Two different methods ( Method I and Method 2) have been proposed based on the Sμ and Sμ (E-1) to describe the maximum mass burning rate given as, mb = ASμpμ=CdeA(2pPμred)o.5 mb =ASgPm =AgSμ(E-I)P μ=Cde4,(2pu Pred)0,5 (2) The equation given in (2) is slightly different from (1) as is about 6.5 times the mass flow of the first method as it takes the effect of (E-1) where E is the expansion ratio. A critical review were carried out for the applicability, validity and limitation on the venting correlations adopted in NFPA 68 and European Standard with 470 literature experimental data, covering a wide range of values for vessel volume and geometries, bursting vent pressure, Pv L/D ratio, maximum reduced pressure, Pred and ignition location. The fuels involved are methane, propane, hydrogen, town gas, ethylene, acetone/air mixtures with the most hazardous near-stoichiornetric fuel-air concentration. Besides, Molkov's equation (Molkov, 2001) which is regarded as alternative venting design offered in NFPA 68 and Bradley and Mitcheson's equation for safe venting design were also analysed on the experimental data for their validity and limitation as well as the proposed methods. From the results, it is clear that Bartknecht's equation gave a satisfactory result with experimental data for K <-5 and Swift's equation (Swift, 1983) can be extended to wider range for Pred> 200 mbar, providing the parameter PV is added into the equation. Method 2 gave a good agreement to most of the experimental data as it followed assumptions applied for correlations given by Bradley and Mitcheson for safe venting design (Bradley and Mitcheson, 1978a,B radley and Mitcheson, 1978b). It is also proven that the vent coefficient, K is confident to be used in quantifying the vessel's geometry for cubic vessel and the use of As/Av term is more favourable for non-cubic vessels. To justify the validity and applicability of the proposed methods, series of simply vented experiments were carried out, involving two different cylindrical volumes i.e. 0.2 and 0.0065 M3. It is found that self acceleration plays important role in bigger vessel in determining the final Pmax inside the vessel. Method 2 gave closer prediction on Pmax in respect with other studied correlations. The investigation of vented gas explosion is explored further with the relief pipe been connected to the vessel at different fuel/air equivalence ratios, ignition position and Pv. The results demonstrate that the magnitude of Pmax was increased corresponding to the increase of Pv- From the experiments,it is found that peak pressure with strong acoustic behaviour is observed related to increase in Pv and in some cases,significant detonation spike was also observed particularly in high burning velocity mixtures. It is found that substantial amount of unburnt gases left inside the vessel after the vent burst is the leading factor in increase of Pmax for high burning velocity mixtures at centrally ignited. The associate gas velocities ahead of the flame create high unburnt gas flows conditions at entry to the vent and this give rise to high back pressures which lead to the severity in final Pmax inside the vessel. It was observed that end ignition leads to a higher explosion severity than central ignition in most cases, implying that central ignition is not a worst-case scenario in gas vented explosions as reported previously.
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Messedi, Nouri. "Contribution à l'étude du comportement d'un moteur à taux de compression variable alimenté au méthane." Valenciennes, 1986. https://ged.uphf.fr/nuxeo/site/esupversions/0f357994-0e2f-428c-be57-1551bb305d52.
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Une partie expérimentale étudie l'influence de la richesse du mélange carburant et des paramètres de fonctionnement d'un moteur monocylindre, quatre temps sur la combustion et les conditions d'apparition du cliquetis en faisant une comparaison méthane/super carburant. Cette étude est complétée par le développement d'un programme de calcul du cycle théorique qui permet de déterminer les pressions et températures ainsi que l'évolution des produits de combustion au cours du cycle.
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Sauvan, Pierre-Emmanuel. "Etude des phénomènes physiques associés à la propagation d'ondes consécutives à une explosion et leur interaction avec des structures, dans un environnement complexe." Phd thesis, Université d'Orléans, 2012. http://tel.archives-ouvertes.fr/tel-00802429.
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Les travaux présentés dans ce mémoire de thèse s'inscrivent dans le cadre des études liées aux dégâts sur les structures et les blessures subies par les personnes à la suite d'explosions de charges explosives en milieu confiné et semi-confiné. Afin de mener cette étude, des expériences sont réalisées à petite échelle en laboratoire et sont complétées par des simulations numériques. Les ondes de choc sont obtenues grâce à la détonation d'une charge explosive gazeuse composée de propane-oxygène en proportion stoechiométrique. L'étude consiste donc à réaliser des expériences à petite échelle en laboratoire afin d'apprécier les champs de pression obtenus à la suite de la détonation d'une charge explosive au sein de deux configurations différentes. La première représente un atelier pyrotechnique et la seconde met en jeu un entrepôt de stockage de bouteilles de gaz. Les résultats expérimentaux sont ensuite confrontés à des résultats obtenus par simulations numériques réalisées grâce au logiciel AUTODYN. En complément de ces deux configuration principales, une étude est menée sur l'identification des pics de surpressions réfléchis grâce à une approche expérimentale appelée paroi par paroi. Une étude est également menée sur la détermination d'une équivalence massique entre le TNT et le mélange gazeux utilisé pour les expériences.
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Kristoffersen, Kjetil. "Gas explosions in process pipes." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-235.
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<p>In this thesis, gas explosions inside pipes are considered. Laboratory experiments and numerical simulations are the basis of the thesis. The target of the work was to develop numerical models that could predict accidental gas explosions inside pipes.</p><p>Experiments were performed in circular steel pipes, with an inner diameter of 22.3 mm, and a plexiglass pipe, with an inner diameter of 40 mm. Propane, acetylene and hydrogen at various equivalence ratios in air were used. Pressure was recorded by Kistler pressure transducers and flame propagation was captured by photodiodes, a SLR camera and a high-speed camera. The experiments showed that acoustic oscillations would occur in the pipes, and that the frequencies of these oscillations are determined by the pipe length. Several inversions of the flame front can occur during the flame propagation in a pipe. These inversions are appearing due to quenching of the flame front at the pipe wall and due to interactions of the flame front with the longitudinal pressure waves in the pipe. Transition to detonation was achieved in acetylene-air mixtures in a 5 m steel pipe with 4 small obstructions.</p><p>Simulations of the flame propagation in smooth pipes were performed with an 1D MATLAB version of the Random Choice Method (RCMLAB). Methods for estimation of quasi 1D burning velocities and of pipe outlet conditions from experimental pressure data were implemented into this code. The simulated pressure waves and flame propagation were compared to the experimental results and there are good agreements between the results.</p><p>Simulations were also performed with the commercial CFD code FLACS. They indicated that to properly handle the longitudinal pressure oscillations in pipes, at least 7 grid cells in each direction of the pipe cross-section and a Courant number of maximum 1 should be used. It was shown that the current combustion model in FLACS gave too high flame speeds initially for gas explosions in a pipe with an inner width of 40 mm.</p>
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Wu, Yajue. "The gas dynamics of venting explosions." Thesis, University of Sheffield, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297677.
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Willacy, Sarah. "Homogeneous and stratified vented gas explosions." Thesis, University of Leeds, 2008. http://etheses.whiterose.ac.uk/1584/.
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Explosion tests were carried out in four medium-scale test-vessels incorporating closed, vented, duct vented and interconnected vessels. A systematic investigation into the influence of homogeneous and stratified mixtures was undertaken by varying mixture reactivity, ignition position, injection position and mixture composition. A feature of this work has been the similarities in explosion phenomena between stratified and homogeneous explosions and between partially filled and fully filled geometries to the conclusion that the explosion severity recorded in stratified mixtures towards the lean flammability limit was in many cases much higher than the fuel concentration would normally suggest. Stratified mixtures with global equivalence ratio around stoichiometric produced significantly lower pressures than their homogeneous equivalents. However, stratified (globally) near-limit mixtures produced overpressures that were several hundred mbar higher than those of the equivalent homogeneous mixtures. Even beyond the flammable range (globally) the stratified mixtures produced significant overpressures. The phenomena discussed in this thesis illustrate the difficulty in designing adequate protection for such vented, duct vented and interconnected geometries, since even relatively small pocket of weak fuel-air mixtures produced relatively severe explosions. This can have implications for the safety design of inter-connected installations which are not intended to be subject to flammable mixtures. While it is an important conclusion from the work presented in this chapter that close to the flammability limits the stratified explosion severity was greater than its global concentration would normally indicate, it should be stressed that homogeneous stoichiometric tests still constitute the worst case tests. Therefore, it is not the suggestion of this work that the design of vented vessels should be modified to represent the maxima obtained in stratified work. However, the value of this research in the field of post-explosion investigation is clear.
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Craft, Neil Hirsh. "An experimental study of hybrid explosive dust-gas-air mixtures /." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66071.
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Matsumoto, Kazuhiro. "Boundary curvature effects on gas bubble oscillations in underwater explosion." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA308087.
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Lewthwaite, Jeni L. "Fire and explosion modelling on offshore oil and gas platforms." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/7850.
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Torrado, David. "Effect of carbon black nanoparticles on the explosion severity of gas mixtures." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0199/document.
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Les explosions de mélanges de gaz inflammables/solides combustibles ne sont pas bien comprises en raison de la complexité des transferts thermiques, des mécanismes de cinétiques et des interactions entre la turbulence /combustion. L'objectif principal de ce travail est d'étudier la sévérité des explosions des nanoparticules de carbone noir/méthane afin de comprendre l'influence de l'insertion des nanoparticules sur les explosions de gaz. Des tests ont été effectués sur ces mélanges dans un tube de propagation de la flamme et dans une sphère d'explosion standard de 20 L. L'influence de la turbulence initiale et de la taille de particule élémentaire du noir de carbone a également été étudiée. Il semble que l'insertion de nanoparticules de noir de carbone augmente d'environ 10% la sévérité de l’explosion pour les mélanges pauvres en méthane. Par conséquent, il semble que les nanoparticules ont un impact sur la sévérité de l'explosion même pour les systèmes à basse turbulence, contrairement aux systèmes impliquant des poudres de taille micrométrique qui nécessitent une dispersion à des niveaux élevés de turbulence. L'augmentation de la vitesse maximale de montée en pression est plus élevée pour des poudres avec un petit diamètre de particule, notamment en raison des phénomènes de fragmentation. En outre, un modèle numérique de propagation de front de flamme associé à un mélange gaz/noir de carbone a été développé pour examiner l'influence du noir de carbone sur la propagation de la flamme. Les résultats du modèle numérique suggèrent que la contribution de la chaleur radiative favorise l'accélération de la flamme. Ces résultats sont en accord avec les résultats expérimentaux de sévérité de l'explosion pour certains mélanges hybrides<br>Flammable gas/solid hybrid mixture explosions are not well understood because of the interaction of the thermal transfer process, the combustion kinetics mechanisms and the interactions between turbulence and combustion. The main objective on this work is to study the explosion severity and flame burning velocities of carbon black nanoparticles/methane to better understand the influence of added nanopowders in gas explosions. Tests have been performed in a flame propagation tube and in the standard 20 L explosion sphere. The influence of carbon black particles on the explosions severity and in the front flame propagation has been appreciated by comparing the results obtained for pure gas mixtures. It appeared that the carbon black nanoparticles insertion increases around 10% the explosion severity for lean methane mixtures. Therefore, it seems that nanoparticles has an impact on the severity of the explosion even for quiescent systems, contrary to systems involving micro-sized powders that requires a dispersion at high turbulence levels. The increment on the maximum rate of pressure rise is higher for powders with lower elementary particle diameter, which is notably due to the fragmentation phenomena. A flame propagation numerical model associated to a gas/carbon black mixture has been developed to examine the influence of carbon blacks on the flame propagation. The results of the numerical model suggest that the radiative heat contribution promotes the flame acceleration. This result is consistent with the experimental increase on the explosion severity for some hybrid mixtures
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Na'inna, Abdulmajid Muhammed. "Effects of obstacle separation distance on gas explosions." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5856/.
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The separation distance (pitch) between obstacles is an area that has not received adequate attention by gas explosion researchers despite general recognition of the important role it plays in determining the explosion severity. Either too large or too small a separation distance between the obstacles would lead to lower explosion severity. Therefore obstacles would need to have “optimal” separation distance to produce the worst case explosions overpressures and flame speeds. Most studies to date with multi-obstacles had the obstacles too closely packed resulting in data that most likely do not represent the worst case scenarios. The major objective of this project was to investigate the influence of spacing between obstacles in gas explosions by systematically varying the distance in order to determine the worst case separation that will produce the maximum explosion severity. A long vented cylindrical vessel 162 mm internal diameter with an overall length to diameter ratio (L/D) of 27 was used in the experimental study. The vessel was closed at the ignition end and its open end connected to a large cylindrical dump-vessel with a volume of 50 m3. The spacing between the obstacles in the test vessel was systematically varied from 0.25 m to 2.75 m. The influence of obstacle spacing was studied with obstacles of different blockage ratios, shapes, number and scale. Tests were carried out with methane, propane, ethylene and hydrogen mixtures with air. A correlation was developed and applied in this research to predict the position to maximum intensity of turbulence downstream of an obstacle, xmax dimensionalised with obstacle scale, b as a function of obstacle blockage ratio, BR, using steady state experiments from the limited available data in the literature as, ( ) for t/d < 0.6 (thin/sharp obstacles) A clearly defined separation distance which gave the most severe explosions in terms of both maximum flame speed and overpressure was found in this research. The profile of effects with separation distance agreed with the cold flow turbulence profile determined in cold flows by other researchers. However, the present results showed that the maximum effect in explosions is experienced further downstream than the position of maximum turbulence determined in the cold flow studies. It is suggested that this may be due to the convection of the turbulence profile by the propagating flame, after the flame has moved passed the obstacle. The predicted model on position to maximum intensity of turbulence from cold flow data agreed with the worst case obstacle separation distance in the current research if multiplied by a factor of three. Turbulence parameters were estimated from pressure differential measurements and geometrical obstacle dimensions. This enabled the calculation of the explosions induced gas velocities, r.m.s turbulent velocity, turbulent Reynolds number and Karlovitz number. By expressing these parameters in terms of turbulent combustion regimes, the bulk of the tests in this study was shown to be within the thickened-wrinkled flames regime. Turbulent burning velocity, ST models with dependence on obstacle scale, higher than the ones in the existing gas explosion scaling techniques were obtained as, for single hole-obstacles for single flat-bar obstacles From the newly obtained ST correlation for single flat-bar obstacles, an overpressure correlation, P for scaling relationship was derived and validated against both small and large scale experimental data and the results were encouraging. [( √ ) ][ ] In planning the layout of new installations, it is appropriate to identify the relevant worst case obstacle separation in order to avoid it. In assessing the risk to existing installations and taking appropriate mitigation measures it is important to evaluate such risk on the basis of a clear understanding of the effects of separation distance and congestion. The present research would suggest that in many previous studies of repeated obstacles the separation distance investigated might not have included the worst case set up, and therefore existing explosion protection guidelines may not correspond to worst case scenarios.
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van, Herel Ryan Marinus Johannes Wilhelmus Maria. "Wire Explosion via Electromagnetic Induction." Thesis, University of Canterbury. Electrical and Computer Engineering, 2011. http://hdl.handle.net/10092/6719.
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This research is aimed at exploding a wire via electromagnetic induction, with a preference for obtaining restrike of the exploding wire in a ring shape or otherwise.
Literature on both exploding wire and electromagnetic induction are introduced together. A mathematical framework to describe the wire explosion by induction is formulated from first principles using the idea of magnetic flux linkages. The environment in which the experiments took place is described, with reference to matters of laboratory safety and also measurement of transient electrical current and voltage in the wire explosion by induction. The results describe the approaches taken to explode a wire by induction to obtain a plasma conductor. Voltage and current data
are displayed and described. Throughout this work, there are long-exposure digital photographic images of the experiments taking place. These contribute to determining the outcome of experiments, and support the conclusions. Wires were exploded
by induction in an air-cored mutually coupled coils system, and restrike of those wires was achieved. Electrical characteristics of wire explosion by electromagnetic induction are displayed and discussed based on what is known about straight exploding
wires. Future works involving creation of plasma rings, electromagnetic thrust and exploding wires in vacuum are discussed.
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Mohsen, Yehya. "Conception et caractérisation d’une plate-forme microfluidique pour la détection sélective de traces d’un produit de dégradation du TNT dans l’atmosphère." Thesis, Besançon, 2013. http://www.theses.fr/2013BESA2004/document.
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L’objectif de cette étude est de concevoir et caractériser une plate-forme micro-fluidique permettant la concentration et la séparation d’un produit de dégradation du trinitrotoluène :l’ortho-nitrotoluène (ONT) considéré comme un traceur de composés explosifs. Les capteurs àbase de dioxyde d’étain (SnO2) utilisés ici comme détecteurs présentent un réel manque desélectivité et leur sensibilité peut s’avérer insuffisante pour la détection de traces de polluantsdans l’atmosphère. L’approche originale envisagée dans cette étude consiste à travailler en amontdu capteur chimique (SnO2), en particulier, en développant d’une part un micro-préconcentrateurde gaz afin d’améliorer l’aspect sensibilité et d’autre part une micro-colonne chromatographiquepour s’affranchir du manque de sélectivité.Dans un premier temps, une série d’adsorbants ont été étudiés et caractérisés pour laconcentration de l’ONT. Les résultats obtenus ont permis de sélectionner trois types de charbonsactifs (N, KL2 et KL3) et une zéolithe hydrophobe DAY.Ensuite, les micro-systèmes fluidiques ont été réalisés sur un substrat de silicium et élaborés enutilisant la technologie silicium/verre.La dernière partie de ce travail est consacrée à l’évaluation des performances d’analyse de cetteplate-forme en termes de concentration et de séparation de l’ONT. En particulier, après avoirévalué les conditions optimales de concentration et d’élution de l’ortho-nitrotoluène, le couplageentre la plate-forme micro-fluidique et le capteur à base de dioxyde d’étain a permis d’une part demontrer que la limite de détection de l’ortho-nitrotoluène est inférieure à 365 ppb. Dans ce cas,une désorption totale de la molécule cible et un facteur de concentration constant ont été obtenusavec la zéolithe DAY. D’autre part, l’utilisation de ce type de plate-forme a permis d’obtenir unebonne performance de détection et de séparation de l’ONT en présence d’un interférent (toluène)et d’un taux d’hygrométrie élevé<br>The objective of this study is to develop and characterize a micro-fluidic platform allowing theconcentration and the separation of a degradation compound of trinitrotoluene: the orthonitrotoluenerecognized as an explosive taggants. Tin dioxide gas sensors (SnO2) used here asdetectors suffer from a luck of selectivity and have an insufficient sensitivity toward most ofpollutants. For that, our original approach consists to work in front of a chemical gas sensor(SnO2), in particular, by developing on the one hand a gas micro-preconcentrator to improve thesensitivity and on the other hand, a chromatographic micro-column in order to overcome the luckof selectivity.First, various adsorbents have been studied and characterized for the ONT concentration. Theobtained results allowed to select three types of activated carbons (N, KL2 and KL3) and ahydrophobic zeolite DAY. Then, the micro-system devices have been realized on a siliconsubstrate and manufactured using the silicon/glass technology.The last part of this work is devoted to the evaluation of the platform performances in terms ofconcentration and separation of ONT. In particular, after the optimization of the experimentalconditions concerning the concentration and the elution of ortho-nitrotoluene, the couplingbetween the micro-fluidic platform and a tin dioxide gas sensor allowed on the one hand to showthat the detection limit of the ONT pollutant is lower than 365 ppb. In this case, a total desorptionof the analyte and a constant concentration factor were obtained with the zeolite DAY. On theother hand, the use of this type of platform allowed to obtain a good separation and detectionperformance of ONT in presence of interferent (toluene) and at high humidity rate
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Dounia, Omar. "Numerical investigation of gas explosion phenomena in confined and obstructed channels." Phd thesis, Toulouse, INPT, 2018. http://oatao.univ-toulouse.fr/20584/1/DOUNIA_Omar.pdf.
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Mining, process and energy industries suffer from billions of dollars of worldwide losses every year due to Vapour Cloud Explosions (VCE). Moreover, explosion accidents are often tragic and lead to a high number of severe injuries and fatalities. The VCE scenario is complex and controlled by various mechanisms. The interplay among them is still not entirely understood. Understanding all these intricate processes is of vital importance and requires detailed experimental diagnostics. Coupling accurate numerical simulations to well documented experiments can allow an elaborate description of these phenomena. This thesis focuses on explosions occurring on configurations that are either semi-confined or confined. In such configurations, the explosion is generally initiated by a mild ignition and a subsonic flame front emerges from the ignition source. An important feature of self-propagating flames lies in their intrinsically unstable nature. When they propagate in an environment with high levels of confinement and congestion, which is the case in most industrial sites, a Flame Acceleration (FA) process is often observed that can give rise to very fast flames, known for their destructive potential. In some cases, the FA process can create the appropriate conditions for the initiation of detonations, which corresponds to a rapid escalation of the explosion hazard. To reproduce the confinement and congestion conditions that one can find in industrial sites, the university of Munich TUM equipped a confined chamber with a series of obstacles and analysed the influence of repeated obstructions on the propagation of hydrogen/air deflagrations. This experimental study showed a strong influence of the mixture composition on the acceleration process. A Deflagration to Detonation Transition (DDT) has also been observed for a certain range of equivalence ratio. This configuration is therefore ideal to study the mechanisms of flame acceleration as well as the intricate DDT process. A numerical study of both scenarios is performed in this thesis: -First for a lean premixed hydrogen/air mixture, a strong flame acceleration is observed experimentally without DDT. The characteristic features of the explosion are well reproduced numerically using a Large Eddy Simulation (LES) approach. The crucial importance of confinement and repeated flame-obstacle interactions in producing very fast deflagrations is highlighted. -DDT is observed experimentally for a stoichiometric hydrogen/air mixture. This thesis focuses on the instants surrounding the DDT event, using Direct Numerical Simulations (DNS). Particular attention is drawn to the impact of the chemistry modelling on the detonation scenario. The failure of preventive measures is often observed in many explosion accidents. To avoid a rapid escalation of the explosion scenario, mitigative procedures must be triggered when a gas leak or an ignition is detected. Metal salts (like potassium bicarbonate and sodium bicarbonate) have received considerable attention recently because well-controlled experiments showed their high efficiency in inhibiting fires. The last part of the thesis focused on the mechanism of flame inhibition by sodium bicarbonate particles. First, criteria based on the particle sizes are established to characterize the inhibition efficiency of the particles. Second, two dimensional numerical simulations of a planar flame propagating in a stratified layer of very fine sodium bicarbonate particles showed that under certain conditions these powders can act as combustion enhancers. These results echo a number of experimental observations on the possible counter-effects of the inhibitors.
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El, Messoudi Abdelmalek. "Modélisation des détonations thermonucléaires en plasmas stellaires dégénérés: applications aux supernovae de types Ia." Doctoral thesis, Universite Libre de Bruxelles, 2008. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210461.
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Plusieurs évènements astrophysiques comme les novae, les supernovae de type Ia (SNeIa) et les sursauts X sont le résultat d'une combustion thermonucléaire explosive dans un plasma stellaire. Les supernovae comptent parmi les objets astrophysiques les plus fascinants tant sur le plan théorique que sur celui des observations. Au moment de l'explosion, la luminosité d'une supernova peut égaler celle de l'intégralité des autres étoiles de la galaxie. On admet aujourd’hui que les SNeIa résultent de l'explosion thermonucléaire d'une étoile naine blanche, un objet dense et compact composé de carbone et d'oxygène. Divers chemins évolutifs peuvent conduire à l’explosion de la naine blanche si celle-ci est membre d’un système stellaire binaire. Néanmoins, la nature du système binaire, les mécanismes d'amorçage et de propagation de la combustion thermonucléaire ainsi que le rapport carbone/oxygène au sein de l'étoile compacte ne sont pas encore clairement identifiés à ce jour. En ce qui concerne l’écoulement réactif, on invoque ainsi une détonation (Modèle sub-Chandrasekhar), une déflagration ou la transition d'une déflagration vers une détonation (Modèle Chandrasekhar). La détonation semble donc jouer un rôle prépondérant dans l'explication des SNeIa. <p>Les difficultés de modélisation des détonations proviennent essentiellement (i) de la libération d'énergie en plusieurs étapes, de l’apparition d’échelles de temps et de longueurs caractéristiques très différentes (ii) des inhomogénéités de densité, de température et de composition du milieu dans lequel se propage le front réactif et qui donnent naissance aux structures cellulaires et autres instabilités de propagation du front (extinctions et réamorçages locaux). <p>En plus de celles citées ci-dessus, deux autres difficultés majeures inhérentes à l'étude de ce mode de propagation dans les plasmas stellaires sont rencontrées :la complexité de l’équation d’état astrophysique et la cinétique nucléaire pouvant impliquer plusieurs milliers de nucléides couplés par plusieurs milliers de réactions. Ainsi, les premiers travaux impliquant une combustion thermonucléaire explosive ont été réalisés sur bases d'hypothèses simplificatrices comme l'équilibre nucléaire statistique instantané des produits de réactions ou l'utilisation d'un réseau réduit à une dizaine d'espèces nucléaires. Dans tous ces travaux, la détonation est assimilée à une discontinuité totalement réactive (détonation de Chapman-Jouguet ou CJ). La résolution de l'onde de détonation nécessite l'étude détaillée du processus nucléaire se déroulant dans la zone de réaction. Malheureusement, les supports de calculs actuels ne permettent pas encore ce type de simulations pour les détonations astrophysiques. Le modèle ZND qui constitue une description unidimensionnelle stationnaire de l’écoulement (plan ou courbé) constitue une excellente approximation de la réalité. <p>Notre travail réexamine les résultats des calculs des structures des ondes de détonations stellaires dans les conditions de température, de densité et de composition envisagées dans les travaux de ce type (détonation CJ et ZND) réalisés jusqu’à présent mais avec une équation d’état appropriée aux plasmas stellaires et une cinétique nucléaire nettement plus riche ;le plus grand réseau jamais utilisé pour ce genre d’études (333 noyaux couplés par 3262 réactions), prenant en compte les données les plus récentes de la physique nucléaire (vitesses de réaction et fonctions de partition)./Several astrophysics events like novae, supernovae and X burts, result from an explosive thermonuclear burning in stellar plasma. Type Ia Supernovae (SNeIa) count amoung the most fascinating stellar objects, they can be more brighter than an entire galaxy. Astrophysic works show that SNeIa may result from a thermonuclear explosion of a compact and dense star called carbon-oxygen white dwarf. The ignition stage and the propagation mode of the thermonuclear combustion wave are not identified yet. The Deflagration-to-Detonation Transition process (or "delayed detonation") sims to give the best overall agrements with the observations :detonations can play appart in SNeIa events. <p><p>Simulating thermonuclear detonations count same difficults. The most important are the burning length scales that spent over more than ten oders of magnitud, the nuclear kinetics that involve thousands of nuclids linked by thousands of nuclear reactions and the stellar plasma equation of state (EOS). Hydrodynamical simulations of detonation use very simplified ingedients like reduced reactions network and asymptotic EOS of completely electron degenerate stellar plasma.<p><p>Our work is the modelling of these detonations using more representative EOS of the stallar plasma that includs ions, electrons, radiation and electron-pistron pairs. We also use a more <p>detailed kinetic network, comprising 331 nuclids linked by 3262 capture and photodisintegration reactions, than those usualy employed.<p> <p><br>Doctorat en Sciences<br>info:eu-repo/semantics/nonPublished
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Knudsen, Vegeir. "Hydrogen gas explosions in pipelines - modeling and experimental investigations." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Fakultet for ingeniørvitenskap og teknologi, 2007. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1572.
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Gas explosions in closed pipes with a single obstacle have been investigated both numerically and experimentally. Most of the work is related to hydrogen and air mixtures, but other fuels have also been used. At the present time there does not exist a software tool or a numerical method that single-handedly can cover the whole range of phenomena in gas explosions. Computational fluid dynamics is also a developing field, even for fluid flow without chemical reactions. The objective of this work was to develop numerical models that can be applied in predictive simulations of gas explosions in pipes and tunnels. Such predictive tools are important since they can expand the knowledge of gas explosions and thereby reduce the risk and consequences of gas explosion accidents. The experiments were performed with premixed fuel and air at atmospheric conditions in three closed steel pipes. The pipes had an inner diameter of 107 mm and inner lengths of 3.0, 4.0 and 7.0 m. The various gas mixtures were ignited at the center of one end wall by a weak ignition source. Both the 4.0 and the 7.0 m pipe had an obstacle installed inside the pipe 1.0 m from the ignition wall. Four different fuels and seven different obstacles were used in the experiments. The obstacles had opening diameters ranging from 5 to 80 mm and the fuels were hydrogen, propane, methane and blends of hydrogen and carbon monoxide. Two types of Kistler pressure transducers were distributed along the pipes to measure the experimental overpressure. The experimental work has provided a unique data set which includes combustion regimes ranging from laminar flames to detonations. Several conditions which affect the flame propagation and transition to detonation in single obstructed pipes have been found. The numerical work has been related to the one dimensional code RCMLAB. New numerical models have been developed and applied in the numerical simulations with this code. (The primary focus of these simulations were the flame propagation between the ignition wall and the obstacle.) The numerical simulations showed a high level of similarity between the measured experimental overpressure and the simulated overpressure at the various pressure transducer positions in the pipe. RCMLAB can therefore be used to enhance the understanding of gas explosions in pipes. Important parameters in the combustion process, such as the average burning rate, can be quantified by this numerical code. The numerical work performed in this thesis have also brought RCMLAB closer to becoming a predictive numerical code for simulation of gas explosions in pipes and tunnels.
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GUIBERT-DUPLANTIER, CATHERINE. "Etude des effets mécaniques des explosions de gaz sur des structures de formes simples." Poitiers, 1993. http://www.theses.fr/1993POIT2342.
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L'etude concerne les effets produits sur l'environnement par l'explosion aerienne, en regime de deflagration, d'une charge gazeuse hemispherique de rayon fini, amorcee en son centre. La composition du melange combustible permet de faire varier la puissance de l'explosion. Le but de ce travail a ete d'apporter des precisions: i) sur l'evolution de la celerite de la deflagration pendant sa phase de ralentissement et d'arret sur le bord de la charge en fin d'explosion; ii) sur l'interaction de l'onde de pression, associee a la deflagration, avec des structures de formes simples (plaques, cubes, cylindres, spheres). Une loi empirique a ete proposee pour caracteriser le ralentissement et l'arret de la flamme en fin d'explosion. Cette loi de ralentissement et d'arret a permis d'estimer la phase negative de l'onde de pression et en particulier son amplitude maximale qui est comparable a celle de la surpression maximale atteinte au cours de l'explosion. Les variations de pression supportees par une structure placee dans le champ de l'explosion, ont ete mesurees en differents points de sa paroi. La pression incidente est amplifiee sur la surface de l'obstacle directement exposee au souffle de l'explosion et attenuee sur la surface cachee. Les coefficients caracterisant cette amplification (ou cette attenuation) dependent de la localisation du point sur l'obstacle mais aussi de la taille et de la forme de ce dernier. Ils varient peu avec la distance de l'obstacle au centre de l'explosion. L'amplification et l'attenuation des effets de l'onde incidente sont augmentees lorsqu'on modifie la forme de la structure dans l'ordre suivant: sphere-cylindre-plaque-cube. L'ensemble des resultats exposes trouve son application dans le domaine de l'analyse et de la prevention des risques d'explosion sur un site industriel
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Lemetayer, Julien. "Etude par PIV par fluorescence de l’interaction d’un spray avec un écoulement gazeux en aérodynamique contrôlée : application à l’injection directe essence." Thesis, Rouen, INSA, 2016. http://www.theses.fr/2016ISAM0023/document.
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De nombreux procédés actuels mettent en jeu des écoulements diphasiques (sprays agricoles, pharmaceutiques, peinture...). Néanmoins, la connaissance des mécanismes régissant les interactions entre les phases (entraînement, modification des trajectoires des particules, transfert d'énergie...) est encore incomplète, notamment lors de l'injection directe essence, qui représente le cadre de cette étude. Dans cette étude expérimentale, les dynamiques instantanées des deux phases sont étudiées dans un plan pour mettre en évidence les interactions aérodynamiques entre les phases. Pour ce faire, un diagnostic de FPIV diphasique, utilisant un colorant fluorescent pour chaque phase, est développé afin d'acquérir simultanément des images séparées de chaque phase sur deux caméras indépendantes. Ainsi, les vitesses instantanées et simultanées des deux phases sont mesurées sans recourir à un prétraitement des images. Dans un premier temps, ce diagnostic optique est appliqué à la caractérisation d'une injection dans un gaz au repos. L'injection du spray met en mouvement le gaz par le biais d'un transfert de quantité de mouvement du spray vers le gaz. La dispersion des gouttes du spray et le mélange des deux phases qui résultent de ces transferts d'énergie cinétique dépendent du type de spray et également de la pression d'injection. Dans un second temps, ces interactions sont étudiées dans un moteur monocylindre transparent. La comparaison entre les fonctionnements avec et sans injection indique un impact notable de la présence du spray sur l'aérodynamique interne par le développement de nouvelles structures et la modification des caractéristiques du tumble. L'aérodynamique interne du moteur modifie également le développement du spray en comparaison de l'injection dans un gaz au repos<br>Two-phase flows are involved in numerous actual industrial processes (agriculture, pharmacy, painting...). However, the complex interactions between phases (entrainment, particle trajectory modification, energy transfer...) are not well understood, especially for the gasoline direct injection, which represents the context of this study. For this experimental study, instantaneous dynamics of both phases are studied in a plan to highlight the aerodynamic interactions between phases. To achieve that, a two-phase FPIV diagnostic, based on using a fluorescent dye for each phase, is developed to simultaneously acquire separated images of each phase on two independent cameras. Instantaneous and simultaneous velocities of both phases are measured without any image pre-processing. Firstly, this optical diagnostic is applied to the characterisation of a spray injection in a gas at rest. The spray drags the gas by a momentum transfer from spray to gas. The spray droplet dispersion and the mixture between the two phases, which result from this kinetic energy transfer, depend on the spray topology and the injection pressure. Then, these interactions are studied in a transparent monocylinder engine. The comparison between cycles with and without injection reveals a significant impact of the spray presence on the internal aerodynamic through the development of new structures and the modification of tumble characteristics. The internal aerodynamic also modifies the spray development in comparison to the injection in a gas at rest
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Carazzo, Guillaume. "Nouvelle description physique de la turbulence et implications pour les écoulements volcaniques explosifs." Paris 7, 2007. http://www.theses.fr/2007PA077215.
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Les gaz et les cendres injectés dans l'atmosphère au cours d'une éruption volcanique explosive représentent une menace pour les populations, les biens et l'environnement. Cette menace est d'autant plus élevée lorsque le jet volcanique s'effondre sur lui-même et génère des écoulements pyroclastiques. L'étude des éruptions Pliniennes du volcan de la Montagne Pelée révèle que les modèles théoriques de prédiction d'effondrement de colonne souffrent d'un décalage avec les données recueillies sur le terrain. Le but de cette thèse est de comprendre quel est l'ingrédient physique qui manque aux modèles pour être en accord avec les données géologiques. Un nouveau modèle d'entraînement de fluide environnant au sein d'un jet turbulent est présenté. Celui-ci permet de remettre en cohérence de nombreuses données expérimentales sur des jets turbulents générés en laboratoire, et son application à la prédiction d'effondrement de colonnes volcaniques est tout à fait satisfaisante. L'effet nouvellement mis en lumière a une forte influence sur le comportement du jet volcanique et a des implications importantes sur les estimations de flux mis en jeu lors d'éruptions explosives. Pour aller plus loin dans l'étude de la dynamique des colonnes explosives, un dispositif expérimental inédit produisant des jets de gaz chaud chargés en particules a été élaboré. Ce dispositif permet de reproduire pour la première fois le régime d'effondrement partiel où le jet volcanique se sépare en une partie dense et une partie plus légère. Ces résultats apportent une meilleure compréhension de la dynamique d'un jet turbulent en général, et améliorent les modèles théoriques actuels de colonnes volcaniques<br>Gases and ashes injected in the atmosphere during explosive volcanic eruptions are a threat for people, goods and environment. This threat is much higher when the volcanic jet collapses on itself producing pyroclastic flows. The study of the Plinian eruptions of the Montagne Pelee volcano reveals that the theoretical models of column collapse are shifted with the data collected in the field. The aim of this thesis is to understand what is the physical ingredient missing in current models. A new model of entrainment of surrounding fluid within a turbulent jet is presented. This model allows to reconcile several experimental data on laboratory turbulent jets, and its application to the prediction of volcanic column collapse is quite satisfactory. The newly highlighted effect has a strong influence on the volcanic jet behaviour and has important implications on the estimations of fluxes involved during explosive eruptions. To go further in the study of explosive column dynamics, an experimental device producing hot particle-laden jets has been built. This set up allows to reproduce for the first time the transitional regime in which the volcanic jet separates in a dense part and a lighter part. These results provide a better understanding of turbulent jet dynamics, and improve the current theoretical models of volcanic columns
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Wong, C. W. "Numerical modelling of masonry panels subject to loading from gas explosions." Thesis, Middlesex University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337850.
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Johnston, S. A. "Mitigation of gas and vapour cloud explosions using fine water sprays." Thesis, University of Salford, 2015. http://usir.salford.ac.uk/34129/.
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For the past fifty years or so, there has been a great deal of interest in the use of water based explosion suppression systems, designed to mitigate or reduce the impact of thermal explosions and their consequential overpressures, which may be as high as 2MPa in outdoor environments. This level of interest has been heightened in more recent years due to a number of high loss explosion events including, Flixborough, UK (1974), Piper Alpha, North Sea (1998) and Buncefield, UK (2005). All of the previous research has focused on the suppression and mitigation proficiency of existing or new water deluge systems, which deploy sprays containing droplets 200≤D32≤1000μm. Where a high speed flame propagates through a region of spray containing such droplets, the flow ahead of the flame will hydrodynamically break up the droplets into fine mist, which in turn will act as a heat sink in the flame, with a resulting degree of suppression. These studies concluded that in most cases, existing deluge systems contributed to a global reduction in flame speed and thus caused a decrease in the resultant damaging overpressures. This present study however, is focused on the mitigation of slow moving deflagrations with resulting speeds of ≤30m/s. A flame travelling at such low relative speeds will not possess the inertia to inflict secondary atomisation by hydrodynamic break up. Consequently, the droplets within the spray must be small enough to extract heat in the short finite moments that the flame and droplets interact (approximately 0.03ms for a representative 1mm thick flame front). Previous theoretical studies have suggested that droplets, D32, in the order of 10μm - 20μm will be required to successfully mitigate combustion without relying on further droplet break up. To date, there have been no other published experimental studies in this area. An innovative high pressure atomiser known as a Spill Return Atomiser (SRA) was selected, which contained a unique swirl chamber and was originally developed for decontamination and disinfection. The efficient atomisation of the SRA produced fine sprays containing droplets, D32, 15μm - 20μm. A series of „cold trials‟ were conducted to further develop the single SRA, which manifested in the creation of several exclusive single and multiple spray options in counter, parallel and cross flow, with the direction of the propagating flame. These new configurations were supplied with deionised water at a liquid pressure of 13MPa and were qualitatively analysed using High Definition (HD) imagery and quantitatively characterised using non-intrusive laser techniques. During the development stages of this study the SRA spray cone angle was increased from 34.7˚ to 49.2˚and the exit orifice flow rate was raised from 0.295 L/min to 1.36 L/min. The increase in flow rate provided a number of spray options ranging from 17≤D32≤29μm, with liquid volume flux of 0.011 cm3/s/cm2 - 0.047cm3/s/cm2 and mean droplet velocity of 0m/s - 21.4m/s, with the resulting characteristics giving way to complete explosion mitigation qualities. The second phase of this study was to conceive, design and build a suitable apparatus capable of producing slow representative flame speeds within the range of 5 m/s - 30m/s. In excess of 250 mitigation „hot trials‟ were performed using the unique conformations produced during the „cold trials‟, whereby a configuration consisting of 4 x SRA‟s in cross flow (X/F) configuration, successfully and repeatedly, completely mitigated homogeneous methane-air mixtures throughout the whole flammable range E.R. 0.5≤(ϕ)1.0≤ 1.69 (5 - 15%), with flame speeds ranging from 5 - 30m/s. The combined spray configuration consisted of four SRA‟s which were 105mm apart and each opposed by 120˚, thus providing a total spray region of 315mm (spray centre to centre). As the sprays did not overlap or converge, the liquid volume flux remained as 0.047cm3/s/cm2. With droplets, D32, ≤30μm generally requiring impact velocities of approximately ≥142.83m/s to break up further, the flame speeds experienced in these trials of ≤30m/s would not have caused hydrodynamic break up of the droplets in the sprays. Therefore, due to the flame speeds and drop sizes utilised in this study, the droplets entering the flame front would have been in their original form. Although some comparisons were made using the experimental data with Computational Fluid Dynamics (CFD), it proved to be an extremely complicated phenomenon. This was due to the presence and interaction of the complexities of the combustion process and other variables such as water droplet dynamics and heat transfer modes. As such, a set of recommendations have therefore been proposed in pursuing this work in future projects.
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Liatsis, Dimitrios. "Gas induced rupture of elastomers." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47540.
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Concilio, Hansson Roberta. "An Experimental Study on the Dynamics of a Single Droplet Vapor Explosion." Doctoral thesis, KTH, Kärnkraftsäkerhet, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26014.
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The present study aims to develop a mechanistic understanding of the thermal-hydraulic processes in a vapor explosion, which may occur in nuclear power plants during a hypothetical severe accident involving interactions of high-temperature corium melt and volatile coolant. Over the past several decades, a large body of literature has been accumulated on vapor explosion phenomenology and methods for assessment of the related risk. Vapor explosion is driven by a rapid fragmentation of high temperaturemelt droplets, leading to a substantial increase of heattransfer areas and subsequent explosive evaporation of the volatile coolant. Constrained by the liquid-phase coolant, the rapid vapor production in the interaction zone causes pressurization and dynamic loading on surrounding structures. While such a general understanding has been established, the triggering mechanism and subsequent dynamic fine fragmentation have yet not been clearly understood. A few mechanistic fragmentation models have been proposed, however, computational efforts to simulate the phenomena generated a large scatter of results. Dynamics of the hot liquid (melt) droplet and the volatile liquid (coolant) are investigated in the MISTEE (Micro-Interactions in Steam Explosion Experiments) facility by performing well-controlled, externally triggered, single-droplet experiments, using a high-speed visualization system with synchronized digital cinematography and continuous X-ray radiography, called SHARP (Simultaneous High-speed Acquisition of X-ray Radiography and Photography). After an elaborate image processing, the SHARP images depict the evolution of both melt material (dispersal) and coolant (bubble dynamics), and their microscale interactions, i.e. the triggering phenomenology. The images point to coolant entrainment into the droplet surface as the mechanism for direct contact/mixing ultimately responsible for energetic interactions. Most importantly, the MISTEE data reveals an inverse correlation between the coolant temperature and the molten droplet deformation/prefragmentation during the first bubble dynamics cycle. The SHARP observations followed by further analysis leads to a hypothesis about a novel phenomenon called pre-conditioning, according to which dynamics of the first bubble-dynamics cycle and the ability of the melt drop to deform/pre-fragment dictate the subsequent explosivity of the so-triggered droplet. The effect of non-condensable gases on the perceived mechanisms was investigated on the MISTEE-NCG test campaign, in which a considerable amount of non-condensable gases (NCG) are present in the film that enfolds the molten droplet. The SHARP images for the MISTEE-NCG tests were analyzed and special attention was given to the morphology (aspect ratio) and dynamics of the air/ vapor bubble, as well as the melt drop preconditioning and interaction energetics. Analysis showed twomain aspects when compared to the MISTEE test series (withoutentrapped air). First, the investigation showed that the meltpreconditioning still strongly depends on the coolant subcooling. Second,in respect to the energetics, the tests consistently showed a reducedconversion ratio compared to that of the MISTEE test series. The effect of the melt material in the steam explosion triggerability was also summoned, since it would in principle directly implicate the melt preconditioning. Since a number of the thermo-physical properties of the material would influence the triggering process, we focused on the material properties by using the same dioxide material with difference concentrations, i.e. eutectic and non-eutectic. Unfortunately, due to the high melt superheat the possible differences were not perceived. Thus, inaddition to other materials, lower melt superheat tests were schedule inthe future.<br>QC 20101110
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Chisum, James E. "Simulation of the dynamic behavior of explosion gas bubbles in a compressible fluid medium." Diss., Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA326363.
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Dissertation (Ph.D. in Mechanical Engineering) Naval Postgraduate School, December 1996.<br>Dissertation supervisor(s): Young S. Shin. "December 1996." Includes bibliographical references (p. 81-83). Also available online.
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Shearer, Murray J. "Analysis of large-scale gas explosion tests and assessment of potential impact on structures." Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/844451/.
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This document provides a framework for the assessment of gas explosion impact on structures. It shows how the probability of a structure achieving a predefined level of success in withstanding a defined gas explosion scenario may be calculated. The thesis opens with a general introduction to the need for assessing the impact of gas explosions in offshore installations. In the second chapter relevant literature regarding the existing theory and approaches used in assessment of gas explosions is reviewed. In particular, limitations of existing techniques are highlighted. The experimental data that is available to the author is also discussed. In the third chapter a set of objectives is defined. Meeting these objectives would allow many of the outstanding issues in gas explosion assessment, highlighted in chapter two, to be addressed. These objectives essentially define the need for assessment of explosions to relate to the impact upon the structure they engulf and that the impact is dependent not only upon the explosion but upon the structure so effected. The fourth chapter extends an existing technique of applying time-averaging windows to pressure-time histories from explosions. In this chapter, the importance of an approach to analysing explosions that relates directly to structural response is first established. An improved understanding of the effect of explosion parameters upon explosion magnitude is also made. The fifth chapter makes use of conventional signal analysis techniques to address weaknesses of time-averaging approach. These techniques allow a better relationship between identified structural response frequency and quantification of loading to be reached. These techniques also allow analysis of the explosion time history to be made in the frequency domain. Our understanding of the explosion parameters on explosion magnitude is again advanced. Whereas the fifth chapter allows analysis to be made in the frequency pressure domain, the sixth chapter shows how analysis can be made in the frequency-loading domain. This is achieved by assessing the impact of pressure-time histories on a simple oscillating structure, a single degree of freedom object. Of all the techniques developed, this is believed to be the most appropriate. In the seventh chapter we begin to apply the techniques developed by assessing, among other things, the inherent repeatability of an explosion and our ability to accurately predict the magnitude of the explosion. We start to generate a body of statistical data relating to accidental gas explosions. Chapter eight shows how the knowledge gained in previous chapters might be applied within a framework that is relevant to current practices in risk assessment. The framework selected is known as the limit state approach. It is shown how performance criteria for the structure undergoing gas explosions might be set and how the probability of the structure meeting these conditions might be assessed.
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Kang, KiYeob. "Statistical and Probabilistic Risk Assessment for an Induced Gas Explosion on an Offshore Platform." Thesis, Curtin University, 2019. http://hdl.handle.net/20.500.11937/79005.
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The purpose of this research was to investigate the influence of explosion wave on structural integrity in terms of risk assessment concept. It was a computational analysis study that covered how explosion wave pressure could be changed according to several variables, and how dangerous it is in terms of structural physical damage. By using relevant theories and techniques, the extent of explosion risk was assessed based on both quantitative and qualitative methodologies.
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Penlou, Baptiste. "Étude expérimentale des écoulements gaz-particules en contexte de fontaine pyroclastique." Electronic Thesis or Diss., Université Clermont Auvergne (2021-...), 2023. http://www.theses.fr/2023UCFA0159.
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Les colonnes pyroclastiques se forment lors d'éruptions volcaniques explosives au cours desquelles un mélange de gaz et de particules est éjecté à grande vitesse depuis un évent et peut conduire à la formation de panaches convectifs. La stabilité de ces colonnes dépend de divers paramètres qui peuvent varier au cours du temps et causer l'effondrement partiel ou total du mélange pyroclastique. Ces effondrements donnent naissance à des fontaines éruptives à l'origine de courants de densité pyroclastiques (CDPs). L'objectif de cette thèse est double : étudier (1) les mécanismes de sédimentation des particules dans le panache et la partie diluée des CDPs et (2) les mécanismes d'émergence des CDPs dans les zones d'impacts des fontaines. La méthode choisie est l'approche expérimentale.Une première série d'expériences consiste à mettre en suspension des particules de taille variant de 49 à 467,5 µm dans un dispositif cylindrique et à mesurer la concentration locale de particules de chaque mélange. Pour cela, deux approches indépendantes ont été utilisées et ont donné des résultats similaires : une méthode acoustique et l'utilisation des capteurs de pression. Ces expériences mettent en lumière deux mécanismes de sédimentation des particules : la sédimentation améliorée et la sédimentation retardée. Dans les suspensions de petites particules (78 µm), la vitesse de sédimentation augmente avec la concentration locale de particules en raison de la formation de « clusters » qui chutent à une vitesse quatre fois supérieure à la vitesse terminale de sédimentation des particules individuelles (sédimentation améliorée). En revanche, dans les suspensions de plus grandes particules (467,5 µm), la vitesse de sédimentation diminue avec l'augmentation de la concentration de particules malgré la présence de « clusters » et elle est 30 % inférieure à la vitesse de chutes des particules individuelles (sédimentation retardée). Ces résultats suggèrent que les mécanismes de sédimentation en présence de « clusters » et se produisant dans les panaches où la partie diluée des courants de densité pyroclastiques devraient être pris en compte dans les modèles utilisés pour simuler ces phénomènes volcaniques afin de mieux prédire les caractéristiques des dépôts.Une seconde série d'expériences consiste à simuler une fontaine pyroclastique en relâchant dans un chenal des particules de tailles comprises entre 29 et 269 µm et à une hauteur de 3,27 m. Les résultats montrent que les mélanges dilués (1,6 - 4,4 vol.%) en chute libre s'accumulent dans la zone d'impact pour former des écoulements granulaires concentrés (~ 45 - 48 vol.%) dont la pression de fluide interstitiel compense presque totalement le poids des particules pour des tailles < 76 µm. De plus, la pression de fluide maximale mesurée à l'impact, la distance de parcours des écoulements et l'étirement horizontal des dépôts augmentent avec la diminution de taille des particules. En considérant le dimensionnement des expériences, ces résultats indiquent qu'une pression de fluide interstitielle élevée dans les courants de densité pyroclastiques concentrés peut être générée dans la zone d'impact des fontaines pyroclastiques en effondrement. La petite taille des particules, qui cause une faible perméabilité et un long temps de diffusion de la pression de pore, peut être l'un des facteurs principaux qui causent les longues distances parcourues par les écoulements<br>Pyroclastic columns form during explosive volcanic eruptions in which a mixture of gases and particles is ejected at high speed from a vent and can lead to the formation of convective plumes. The stability of these columns depends on various parameters that can vary over time and cause partial or total collapse of the pyroclastic mixture. These collapses give rise to eruptive fountains, forming density currents called pyroclastic density currents (PDCs). The objective of this thesis is twofold: to study (1) the mechanisms of particle sedimentation in the plume and the dilute part of PDCs, and (2) the mechanisms of PDC emergence in the impact zones of the fountains. The chosen method is the experimental approach.A first series of experiments involves suspending particles ranging in size from 49 to 467.5 µm in a cylindrical device and measuring the local particle concentration for each mixture. For this purpose, two independent approaches were used and provided similar results: an acoustic method and the use of pressure sensors. These experiments highlight two mechanisms of particle sedimentation: enhanced sedimentation and delayed sedimentation. In suspensions of small particles (78 µm), the sedimentation rate increases with the local particle concentration due to the formation of « clusters » that fall at a speed four times higher than the terminal settling velocity of individual particles (enhanced sedimentation). However, in suspensions of larger particles (467.5 µm), the sedimentation rate decreases with increasing particle concentration, despite the presence of « clusters » and it is 30 % lower than the settling speed of individual particles (delayed sedimentation). These results suggest that the sedimentation mechanisms in the presence of « clusters » occurring in plumes or the dilute part of PDC should be considered in models used to simulate these volcanic phenomena to better predict deposit characteristics.A second series of experiments simulates a pyroclastic fountain by releasing particles of sizes ranging from 29 and 269 µm into a channel at a height of 3.27 meters. The results show that dilute mixtures (1.6 - 4.4 vol.%) in free fall accumulate in the impact zone to form concentrated granular flows (~ 45 - 48 vol.%) whose interstitial fluid pressure nearly compensates for the weight of particles for sizes < 76 µm. Furthermore, the maximum fluid pressure measured at the impact, the flow travel distance, and the horizontal stretching of deposits increase with decreasing particle size. Considering the experiment dimensions, these results indicate that a high interstitial fluid pressure can be generated in the impact zone of collapsing pyroclastic fountains. The small particle size, causing low permeability and a long pressure diffusion time, may be one of the main factors leading to the long runout distances covered by the flows
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Reiner, George Allen. "An explosive vapor generator based on capillary gas chromatography." Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/39761.
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Bond, Jean-François. "The influence of turbulence on dust and gas explosions in closed vessels /." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65522.
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Cuervo, Rodriguez Nicolas. "Influences of turbulence and combustion regimes on explosions of gas-dust hydrid mixtures." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0300/document.
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Prédire la propagation de la flamme lors d'une explosion de mélanges hybrides poudre/gaz dans des géométries complexes est un défi qui mobilise de multiples ressources. Une approche consiste à déterminer expérimentalement les caractéristiques inhérentes des mélanges poussière-air, comme la vitesse de flamme laminaire, et de les utiliser comme entrées dans les logiciels de Mécanique des Fluides Numérique (CFD). Néanmoins, la caractérisation expérimentale de la vitesse de combustion de suspensions turbulentes de poussières dans l’air est délicate de par notamment la variabilité des propriétés des poudres (taille des particules, humidité...), l'impossibilité de générer un nuage de poussière sans turbulence et l'impact de la poudre sur le rayonnement de la flamme. L’objectif de ce travail était de développer une approche permettant d’évaluer les propriétés fondamentales de propagation des flammes, à partir d'expériences en système fermé et des courbes d'évolution pression-temps, mais surtout grâce à l'analyse de la vitesse de flamme en fonction de son étirement et des instabilités hydrodynamiques. Dans une première étape, la turbulence du nuage de poussière avant inflammation a été étudiée. L'impact de la phase de pyrolyse sur l'explosion de poudres organiques a été aussi souligné expérimentalement et à l’aide d’un modèle de pyrolyse flash. Ensuite, le comportement de mélanges hybrides composés de gaz de pyrolyse et poudres organiques a été analysé, démontrant leurs particularités. Enfin, les interactions turbulence/combustion lors la propagation de la flamme ont été étudiés afin d'en extraire une vitesse de flamme ‘pseudo’ laminaire de la poussière ou des mélanges hybrides<br>Predicting the flame propagation during a dust/gas hybrid mixture explosion in complex geometries is a challenge that mobilizes numerous resources. One approach consists on experimentally determining the inherent characteristics of dust-air mixtures, like the laminar flame speed, and using them as input for Computational Fluid Dynamics (CFD) simulation programs. Nevertheless, the experimental characterization of the burning rates of turbulent dust clouds in air still delicate due to the variability of the properties of powders (particle size distribution, moisture…), the physical impossibility to generate a quiescent dust cloud and the impact of powder on the flame radiation among others. The ultimate goal of this work was to develop an approach to assess fundamental flame propagation properties, from closed vessel experiments and pressure-time evolution curves, but specially from the analysis of flame velocity as a function of its stretching and of the hydrodynamic instabilities. In a first step, the turbulence of the initial dust cloud has been studied. The impact of the pyrolysis phase on organic dusts explosion has also been highlighted both experimentally and by means of model for flash pyrolysis. Furthermore, the explosive behaviour of gas-dusts hybrid mixtures composed of pyrolysis gases and organic dusts has been analysed. Finally, the turbulence/combustion interactions during flame propagation have been studied in order to extract the “pseudo” laminar flame velocity of dusts clouds or hybrid mixtures
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Arntzen, Bjørn Johan. "Modelling of turbulence and combustion for simulation of gas explosions in complex geometries." Doctoral thesis, Norwegian University of Science and Technology, Norwegian University of Science and Technology, 1998. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1481.
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<p>This thesis analyses and presents new models for modelling of turbulent reactive flows for CFD simulation of gas explosions in complex geometries like offshore modules.</p><p>The most important aspects determining the course of a gas explosion in a complex geometry are the development of turbulence and the corresponding increase in the combustion rate during the explosion. To be able to model the process it is necessary to use a CFD code as a starting point, provided with a suitable turbulence and combustion model. The modelling and calculations are done in a 3D finite volume CFD code, where complex geometries are represented by a porosity concept, which gives porosity on the grid cell faces, depending on what is inside the cell.</p><p>The turbulent flow field is modelled with the k-ε turbulence model. The turbulent flow field behind obstructions, which should produce turbulence, is not resolved for smaller geometry. Subgrid models are therefore used for production of turbulence from geometry not fully resolved on the grid. Results from LDA measurements around obstructions in steady and transient turbulent flows have been analysed and the turbulence models have been improved to handle transient, subgrid and reactive flows.</p><p>The combustion is modelled with a burning velocity model, and a flame model which incorporates the burning velocity into the code. Two different flame models have been developed. SIF, which treats the flame as a interface between reactants and products, and the β-model where the reaction zone is resolved with about 3 grid cells.</p><p>The flame normally starts with a quasi laminar burning velocity, due to flame instabilities, modelled as function of flame radius and laminar burning velocity. As the flow field becomes turbulent, the flame uses a turbulent burning velocity model, based on experimental data presented by Bradley, as function of turbulence parameters and laminar burning velocity. The extrapolation of these data is evaluated. The laminar burning velocity is modelled as function of gas mixture, equivalence ratio, pressure and temperature in reactant.</p><p>Pressure/time curves from a range of hydrocarbon gas explosion experiments have been compared with simulations, which in most cases shows good agreement. In simulation of these experiments a range of parameters have been varied, as gas mixture, congestion, obstructions, confinement, scale and grid resolution.</p>
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Mumby, Christopher. "Predictions of explosions and fires of natural gas/hydrogen mixtures for hazard assessment." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/6354.
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The work presented in this thesis was undertaken as part of the safety work package of the NATURALHY project which was an integrated project funded by the European Commission (EC) within the sixth framework programme. The purpose of the NATURALHY project was to investigate the feasibility of using existing natural gas infrastructure to assist a transition to a hydrogen based economy by transporting hydrogen from its place of production to its place of use as a mixture of natural gas and hydrogen. The hydrogen can then be extracted from the mixture for use in fuel cells or the mixture used directly in conventional combustion devices. The research presented in this thesis focused on predicting the consequences of explosions and fires involving natural gas and hydrogen mixtures, using engineering type mathematical models typical of those used by the gas industry for risk assessment purposes. The first part of the thesis concentrated on modifying existing models that had been developed to predict confined vented and unconfined vapour cloud explosions involving natural gas. Three geometries were studied: a confined vented enclosure, an unconfined cubical region of congestion and an unconfined high aspect ratio region of congestion. The modifications made to the models were aimed at accounting for the different characteristics of a natural gas/hydrogen mixture compared to natural gas. Experimental data for the laminar burning velocity of methane/hydrogen mixtures was obtained within the safety work package. For practical reasons, this experimental work was carried at an elevated temperature. Predictions from kinetic modelling were employed to convert this information for use in models predicting explosions at ambient temperature. For confined vented explosions a model developed by Shell (SCOPE) was used and modified by adding new laminar burning velocity and Markstein number data relevant to the gas compositions studied. For vapour cloud explosions in a cubical region of congestion, two models were used. The first model was developed by Shell (CAM2), and was applied using the new laminar burning velocity and other composition specific properties. The second model was based on a model provided by GL Services and was modified by generalising the flame speed model so that any natural gas/hydrogen mixture could be simulated. For vapour cloud explosions in an unconfined high aspect ratio region of congestion, a model from GL Services was used. Modifications were made to the modelling of flame speed so that it could be applied to different fuel compositions, equivalence ratios and the initial flame speed entering the congested region. Predictions from the modified explosion models were compared with large scale experimental data obtained within the safety work package. Generally, (apart from where continuously accelerating flames were produced), satisfactory agreement was achieved. This demonstrated that the modified models could be used, in many cases, for risk assessment purposes for explosions involving natural gas/hydrogen mixtures. The second part of thesis concentrated on predicting the incident thermal radiation from high pressure jet fires and pipelines fires involving natural gas/hydrogen mixtures. The approach taken was to modify existing models, developed for natural gas. For jet fires three models were used. Fuel specific input parameters were derived and the predictions of flame length and incident radiation compared with large scale experimental data. For pipeline fires a model was developed using a multi-point source approach for the radiation emitted by the fire and a correlation for flame length. Again predictions were compared with large scale experimental data. For both types of fire, satisfactory predictions of the flame length and incident radiation were obtained for natural gas and mixtures of natural gas and hydrogen containing approximately 25% hydrogen.